The present invention relates to a sensor and method for sensing precise position of an object, and, more particularly, to techniques and apparatus for selectively reconfiguring a sensor according to any applicable sensing requirements.
Sensors responsive to galvanomagnetic effects, such as Hall or magnetoresistive sensors, are widely used in many applications, including accurate incremental sensing applications, such as sensing the position of an engine crankshaft. For example, accurate engine crank position information may be needed for achieving appropriate ignition timing and state- and federally-mandated detection of engine misfire.
The crank position information may be encoded on a rotating target wheel in the form of teeth and slots. The edges of the teeth may define predetermined crank positions. The sensor is required to detect these edges accurately and repeatably over a range of air gaps and temperatures. Preferably, the output signal of the sensor should indicate a tooth edge passing through the nominal centerline of the sensor, although, a small fixed offset is acceptable. Usually, the specified accuracy is plus or minus 0.5° with respect to the actual edge, which provides a one-degree tolerance band. Quite often, however, fundamentally good sensors with even tighter tolerance bands must be rejected because they do not fall into the specified one-degree tolerance band.
In one basic implementation, a differential sensor may consist of two sensing elements placed some distance apart from each other (e.g., approximately 1–2 mm) with an output signal that comprises the difference of the respective signals from each sensing element. The differential sensor is capable of limiting the error to the plus or minus 0.5° band quite effectively. However, a frequently encountered problem is a shift of this band away from 0°. That is, a shift relative to the actual position of a tooth edge. An example of this shift would be a sensor having its tolerance band shifted from −0.25 degrees to 0.75 degrees in lieu of having a tolerance band from −0.5° to 0.5°. There are multiple causes that may create such a shift. For example, a slight repositioning of the sensor die within a sensor housing during packaging, incremental displacements of the sensing elements during sensor installation, or any combination of the foregoing. In addition, the sensor may have to be located in a location that requires a convoluted geometry and this may lead to a more complex and costly sensor design and manufacturing, which may not be conducive to readily addressing the physical characteristics of the object being sensed, such as spatial separation between tooth edges.